Preheat oven to 375°F. Spray an 8x8-inch baking pan with nonstick spray. Set aside.
In a large bowl, whisk the oats, brown sugar, baking powder, and allspice together.
2¼ cups old-fashioned oats, ½ cup brown sugar, 1 teaspoon baking powder, ¼ teaspoon allspice
In another bowl, mix the half-and-half, eggs, butter, lemon juice, honey, and vanilla extract together until well combined.
2 cups half-and-half, 2 large eggs, 2 tablespoons salted butter, 1 tablespoon lemon juice, 1 tablespoon honey, ½ teaspoon pure vanilla extract
Pour the milk mixture into the oats. Mix well.
Gently fold in the blueberries and pecans.
2 cups blueberries, 1 cup chopped pecans
Transfer the batter into the prepared baking pan and spread it into an even layer.
Bake for 40-45 minutes or until golden brown. Let cool before plating and serving.